The present invention relates to improvements in pump and motor units, especially to units or aggregates wherein a wet electric motor drives the impeller of a glandless centrifugal pump. Such units are used in the boilers of fossel-fired power plants and for many other purposes.
A pump and motor unit must be designed with a view to insure satisfactory operation under normal as well as under certain extreme conditions, for example, such as will arise due to continuously increasing unit output of the plant. Malfunctions of pump and motor units in such plants often arise during starting, when the unit is operated at less than normal load, when the unit is used solely for circulation of liquid and/or during acid cleaning of the boiler or boilers. Additional factors which affect the operation of pump and motor units include high temperatures and/or pressures of conveyed liquids. Still further, the operation of pump and motor units, especially units using glandless pumps and wet motors, can be adversely affected by solid impurities in the circulating fluid medium. Fluids which are circulated by pump and motor units in a fossil-fired power plant or heating plant invariably contain impurities in the form of scale, globules of weldant, rust and/or others. Such impurities are likely to clog the cooling and/or lubricating circuit of the motor, especially the wet motor of a unit which employs a glandless pump. The clogging can result in complete breakdown of the unit and/or the entire plant.
It was already proposed to install a solids-segregating device upstream or downstream of the customary high-pressure cooler in the cooling and/or lubricating circuit of the wet motor. Such proposal has met with little success because the provision of a satisfactory segregating device involves excessive initial and maintenance costs. This will be readily appreciated since the segregating device includes a large number of conduits and valves with attendant problems regarding leakage of circulating fluid. Moreover, the space requirements of a discrete segregating device are excessive in many types of plants which utilize glandless pump and wet motor units. The conduits and valves are likely to develop pockets for entrapped air. Still further, a discrete segregating device must be dismantled, together with the cooling and/or lubricating system, whenever one desires to gain access to the components of the pump and motor unit. Consequently, satisfactory segregation of solid impurities from circulating liquids in accordance with the just discussed proposal creates problems which are often much more serious than the presence of solid impurities.